A. Field of the Invention
This invention relates to directionally solidified eutectic structures and methods, and more particularly to a directionally solidifed eutectic structure having a fiber phase which provides an optical path, the method of forming the same, and applications employing such structure.
B. Description of the Prior Art
It is known in the art that certain eutectic systems when directionally solidified will separate into their constituent components with one component forming a matrix phase and the other component a plurality of fibers. The fibers are generally colinear and distributed in hexagonal array. The diameter of each fiber is inversely proportional to the rate of which the eutectic is solidified, while the density of the fibers distributed within the matrix material is generally proportional to the rate of solidification.
It has been recognized that such fiber arrays would be very useful for optical transmission if light could be made to travel down the fibers and kept out of the matrix. The advantages of such an application stem from the fact that the density of fibers in the eutectic system is greater than that which is presently achievable by bundling together a plurality of discrete optical fibers. The process of forming an array of many fibers by the directional solidification of a single eutectic system is less complicated and offers savings over the formation of individual fibers and subsequent formation of such fibers into a bundle. Also, the typical hexagonal fiber arrangement is very desirable in terms of maximizing fiber density.
Unfortunately, while many different eutectic systems have been directionally solidified to form fibers within a surrounding matrix, the fibers have generally been characterized by a lesser refractive index than the matrix material, and therefor were incapable of containing light. The single known achievement of a fiber optic eutectic microstructure in a prior art was in an Abstract published by the present inventors at the June 1976 American Association of Crystal Growth/West 1976 Meeting. This abstract disclosed a MgF.sub.2 -MgO eutectic system which exhibited optical fibers after directional solidification. The waveguide properties of the system were noted, and its use in conjunction with cathode ray tube (CRT) mosaics and integrated optics was suggested.
While the above specific system represented the first known prior art example of a eutectic system forming an array of optical fibers, the particular system was a type I eutectic. With this type of eutectic system, in which the coupled region does not include the eutectic composition at any except the eutectic temperature, it is considerably more difficult to achieve a satisfactory microstructure than for a type II eutectic system, which includes the eutectic composition at all temperatures. Furthermore, no single eutectic system would be optimal for all optical fiber applications, since the properties of some systems would be expected to be more suitable for certain applications and the properties of other systems more suitable for other applications.
Accordingly, there is still an unsatisfied need for a directionally solidified fiber optic eutectic system of the type II category, as well as a need for a variety of such systems so that a selection may be made between systems to identifiy the ones more suitable for a particular application.